So I was talking to @gewt about Job: A Comedy of Justice ...

So Heinlein had always been very interesting in the short parts of his novels, like the little snippets inside chapters. He had a very fun writing style, and wrote some fun dialogue with fun characters, right?>
It probably comes from how much of his early stuff was short fiction

And I think what happened with a lot of his longer works is that he'd just start writing fun bits and hope it would end up going somewhere or having a bigger plot by the end. like eventually he'd figure out where this was going, then go back and rewrite it into a cohesive whole

and I'm sure he had editors that'd help this process. No editor would let you publish something as rambly and changing-gears-every-other-chapter as The Number Of The Beast, for example... unless you were God-King Of Science Fiction 1980s Robert Heinlein.

so basically I think what happened is that by the 80s (when he was in his seventies!!) he lost the drive to go back and rewrite and he was too Untouchable for editors to make him.

This is combined with his Rules for Writing, (which even if he didn't always live by, certainly explain some of his view on writing) making this worse.

Those rules are:

Rule One: You Must Write
Rule Two: Finish What Your Start
Rule Three: You Must Refrain From Rewriting, Except to Editorial Order
Rule Four: You Must Put Your Story on the Market
Rule Five: You Must Keep it on the Market until it has Sold

and you can see how 2 means that story snippets that don't fit a bigger whole would get finished and published, 3 means he didn't go back and fix this into a longer narrative if no editor is going to demand it, and 4 and 5 mean even "stinkers" get published.

So yeah that explains why these late novels (Number of the Beast, Friday, Job, Cat Who Walks Through Walls, To Sail Behind The Sunset) are so terrible as stories, but here's the thing:
I still love all of these books. I still enjoy them!

and I think that's due to the first part: he was always good at the shorter-form works, and that still shows in the long-form ones. Any given chapter of one of these books is probably still fun to read. Good dialogue, interesting ideas, fun action... it just falls down as a book

so in the short term reading one of these books can be fun and engaging, it's only when you get to the end and look back you realize that this novel went Nowhere and Too Many Places all at once.

it went nowhere because none of this tied into any over-arching plot. This isn't The Moon Is A Harsh Mistress which talks about an emergent AI helping the moon achieve independence and what happens afterwards.

instead some people meet up at a fancy party, have to flee because of hermaphroditic lobster aliens, end up on pseudo-Barsoom, then travel to Alice in Wonderland, Heinlein's other works, then end up in a mega-crossover party where they lock all the Editors in hell!?

that is not a cohesive plot. that's Heinlein having 5 ideas and shoving them all in the same book and not rewriting them together to make sense.

so by having too many ideas it ends up having no singular Idea.
But at the same time, each of those little pieces of the plot? they're okay. not great, but okay.

but then the page-by-page bits of each of those little pieces, those are still great. You can tell that he still had that ability to make fun stories, in the very small scale.

So I think that's why I still enjoy these books. On the small scale, close up, they're fun.

it's just when you zoom out and summarize, when you try to find some conclusion to this long journey, that it really doesn't come out to much. At least not anything that makes any sense.

And I think that his rules for writing really show why:
his approach to writing was very much You Sit Down and you Write The Thing and you tell your agent Publish This Thing and if they come back "The Editor says Fix X" then you Fix X, otherwise you Move On To The Next Thing.

And I think that was a pattern that worked very well for him. His short stories are great. But in longer works, that didn't work so well, especially as he was getting older. I think he stuck to his old habits too much, and really, who could argue with him?

Hey, this isn't very good. You're not going anywhere with this plot, you need to make this fit together better, you need an over-arching narrative of some kind
I'm sorry, I can't hear you over my 11 Hugos, 32 novels, and 59 short stories.

Wait, you only have 4 Hugo awards!
Oh yeah, I forgot to mention: They had to give me seven of those Hugos retroactively because they were for works that I made BEFORE THEY INVENTED THE HUGO

gaining "Protection from Editors" is a failing of many author's later life when they've had a long history of success, so my point here is not to complain that Heinlein's later works suck: plenty of people have made that argument since before I started reading his stuff.

but the more interesting point, I think, is why I (and others, I assume) can still enjoy some of those later novels despite them being objectively terrible.
They're terrible, yes, but only in the bigger picture. They're the sci-fi literature equivalent of the "popcorn flick"

yeah, you walk out of the theater laughing with your friends at how stupid that was, but while you're sitting in the theater, in the moment, the aliens blowing up that building sure was cool, right?

And Heinlein always being good at the dialogue and the short little snippets is something that I think he kept all his life. I dunno why that didn't really decline but the more plot-related parts did. Maybe it was editors, maybe it was failing memory, maybe both.